Field of the Invention
The present invention relates to a driving waveform generating device and a driving waveform generating method for an ink-jet recording head capable of forming dots different in gradation value by driving the recording head according to gradation data, and more particularly to a driving waveform generating device and a driving waveform generating method for an ink-jet recording head capable of generating driving waveforms in a programmable fashion by only changing coordinate data to be prestored.
Related Art
A typical ink-jet printer has a recording head with many nozzles in the subscanning direction (vertical direction) and while paper is fed as designated, the recording head is moved by a carriage mechanism in the main scanning direction (horizontal direction) in order to obtain desired print results. An ink drop is discharged from each nozzle of the recording head at predetermined timing according to dot pattern data resulting from developing the print data fed from a host computer, and the data is printed when the ink drops land on and stick to a print recording medium such as printing paper. Since the ink-jet printer is designed to discharge ink drops or stop to discharge them, that is, designed to control the on-off of dots, it is incapable of directly producing a print output in halftone; namely, gray color and the like. In consequence, there have heretofore been adopted a method of realizing halftone by expressing one pixel with a plurality of dots such as 4.times.4, 8.times.8 and so forth, a technique of increasing the gradient by causing one nozzle to discharge ink drops different in weight dot by dot so as to variably control the dot diameter on printing paper. In order to cause one and the same nozzle to discharge a plurality of ink drops different in weight, it is needed to vary the driving waveform of the head accordingly.
In a conventional driving waveform generating method for an ink-jet recording head, a circuit constituted of a hybrid IC, for example, has been employed so that a desired driving waveform is generated by putting an electric charge in and out of a pressure generating element (piezoelectric vibrator) forming the output side of a head driving circuit in the pulse width modulation (PWM) system (charge pump system).
FIGS. 13 (a), (b) are conceptual drawings of a conventional head driving circuit and the driving waveform formed thereby.
As show in FIG. 13 (a), the conventional head driving circuit is such that a piezoelectric vibrator C for discharging ink drops by displacing itself on receiving voltage forms a capacitor on the output side and is also connected to resistors R1-R6 different in resistance value. The connections of the piezoelectric vibrator C to the resistors R1-R6 are switched by transistors, respectively. The ON/OFF of these transistors are controlled by pulses in the aforesaid PWM system.
With respect to the driving waveform thus generated, the voltage is, as shown in FIG. 13(b), determined by the ON time (pulse width in the PWM system) of each transistor, and its inclination is determined by the CR constant at eth connection of each of the resistors R1-R6 to the aforesaid piezoelectric vibrator C.
In the aforesaid driving waveform generating method using the PWM system, however, the use of a complicated timing pulse is required to obtain the desired waveform.
As obvious from FIG. 13(a), moreover, there has existed a great deal of trouble for regulating timing with respect to variations in component elements such as the resistors R1-R6. In order to obtain more gradation expressions now, it has been attempted to multivalue dots. However, the driving waveform tends to become more complicated if such multivalued dots are employed and this makes it difficult to deal with such a driving waveform in the conventional driving waveform generating system.